3 Hardware Test Setup and Configuration

To evaluate the Audio-to-Haptic performance, a test bench was set up using the DRV2605L and a representative LRA actuator. The hardware consisted of a TI DRV2605LEVM-MD evaluation module (which includes the DRV2605L driver and an LRA on a small board) connected to a host controller. In a real product, the host can be an application processor or microcontroller in the hand-held console. Audio was fed into the DRV2605L and the LRA’s vibration output was observed under various conditions. Key aspects of the setup and configuration included:

• Audio Input and Coupling: An audio codec or signal generator provided an analog audio signal into the DRV2605L’s IN pin. The input was AC-coupled through a 1µF capacitor in series (as recommended) to block any DC offset and allow the AC audio through. The DRV2605L’s input impedance (about 100kΩ) and the 1µF capacitor form a high-pass filter with a cutoff around 1.6Hz, which easily passes the audio frequencies of interest but filters out DC. The audio signal amplitude was kept within the DRV2605L’s acceptable range (no more than about 1.8V_peak-to-peak). In practice, our 100% volume test level corresponded to 1.0VRMS (about 2.8Vp-p), and then scaled down from there for lower percentages. The DRV2605L’s built-in noise gate was left at the default setting, which ignores any audio below a few millivolts – this prevents background hiss or very faint sounds from accidentally triggering the actuator when silence is expected.
• I²C Control and Mode Configuration: The host controller was connected to the DRV2605L’s I²C interface (SCL, SDA). Through I²C commands, the DRV2605L’s registers were configured for Audio-to-Haptic mode. Important register settings included selecting Mode 0x04 (Audio-to-Vibe), enabling LRA drive (as opposed to ERM mode), and enabling analog input with AC-coupling (this involved setting the DRV2605L’s control registers: for example, AC_COUPLE = 1 and N_PWM_ANALOG = 1 in the appropriate control registers). The rated voltage and overdrive clamp were also set for the LRA, but the auto-calibration (described next) can adjust those if needed. Figure 3-1 shows a simplified schematic of the setup, highlighting the connections between the host (application processor), the DRV2605L, and the LRA.
• Auto-Calibration: Before using Audio-to-Haptic mode, the DRV2605L’s auto-calibration routine for the LRA was run. This is a one-time (or infrequent) step that helps the driver measure the LRA’s resonant frequency, rated drive voltage, and other parameters. To do this, the DRV2605L was put in calibration mode (Mode register = 0x07) and the GO bit was toggled through I²C. The driver briefly drives the LRA and measures the response. After a few hundred milliseconds, a status bit indicated the calibration was complete and successful. Auto-calibration set the designed for drive parameters (like the effective resistance and back-EMF constants of the LRA) so that closed-loop control can be accurate for our specific actuator. Calibration was important for the first use of a new LRA; once calibrated, the values were stored in registers and used for subsequent Audio-to-Haptic operation.
• Measurement Instruments: To observe the haptic behavior, a digital oscilloscope (Rigol DS series) with multiple probes was used. One differential probe was connected across the LRA terminals to monitor the voltage being applied to the LRA by the DRV2605L (this differential voltage correlates with the force output of the LRA). Another channel was connected to the audio input signal so the relationship between the audio and the resulting vibration drive can be seen. For evaluating mode switching, the oscilloscope was set to a slower time base (hundreds of milliseconds per division) to capture the moments when modes were toggled. For capturing steady-state waveforms (like the LRA response at a given frequency and amplitude), a faster time base (microseconds to milliseconds scale) was used to see the details of the PWM waveform and the envelope.

The DRV2605L is interfaced to an application processor through I²C (SCL, SDA lines with pull-up resistors). The analog audio input is fed through a coupling capacitor C(IN) into the IN/TRIG pin (with the option to short this to ground if not used). The DRV2605L drives the LRA (or ERM) with a differential output (OUT+ and OUT–); supply decoupling capacitors (C(REG), C(VDD)) are shown for the regulator and supply rails. The EN pin can be used to enable/disable the driver (tie high for always on). The 1µF input capacitor creates a high-pass filter (about 1.6Hz cutoff) with the IN pin impedance, allowing low-frequency audio to pass while blocking DC.

Figure 3-1 Hardware Setup for Testing Audio-to-Haptic Mode

Using this setup, two main sets of experiments were conducted:

1. Steady-State Audio-to-Haptic Performance: Driving the LRA in Audio-to-Haptic mode at various audio frequencies and amplitudes, to characterize how the LRA responds.
2. Mode Switching Tests: Toggling the DRV2605L between Audio-to-Haptic mode and real-time playback mode under different conditions (with and without audio present) to make sure smooth transitions. In the next section, waveform results for the first set of tests (Audio-to-Haptic mode performance) are presented.

Initial I²C Configuration

Before operating the DRV2605L, an initial configuration must be applied through the DRV2605LEVM-MD GUI. Follow these steps:

1. Open DRV2605LEVM-MD GUI and connect the EVM through USB.
2. Select Import Settings and load the provided configuration file (initial table.txt).

The following register settings are essential for proper initialization:

These settings make sure of optimized performance, proper calibration, and mode configuration for Audio-to-Haptic functionality.

Mode-Switching Procedure

After initialization, the DRV2605L can switch between Audio-to-Haptic mode and the built-in library mode dynamically. Use the following I²C commands through GUI's Register Write feature or microcontroller I²C script:

• Switch to Audio-to-Haptic Mode:

Write Register 0x01 = 0x04

• Switch to Built-in Library Mode (Gaming mode):

Write Register 0x01 = 0x00

Write Register 0x0C = 0x01 //Trigger vibration event

To make sure of smooth operation and avoid continuous triggering, follow this timing recommendation:

• Wait approximately 20ms after triggering the vibration event. If no further events occur:

Write Register 0x01 = 0x04 // Return to Audio-to-Haptic mode

This timing makes sure the device transitions smoothly back to continuous audio-derived haptic feedback when explicit events cease.

GUI Usage (DRV2605LEVM-MD)

1. Open the DRV2605LEVM-MD GUI after connecting the evaluation board.
2. Import the provided initial configuration (initial table.txt) using the GUI’s Import Settings button.
3. To switch modes manually:
   • Use the Write option in GUI:
     • Enter Reg= 0x01, Val = 0x04 for Audio-to-Haptic mode.
     • Enter Reg= 0x01, Val = 0x00 for Built-in Library mode.
   • Confirm and execute by clicking the Write button.

This provides a straightforward way to confirm proper DRV2605L operation and quickly evaluate haptic feedback performance under different modes.

Example I²C Script for Automated Testing

For quick and automated testing, you can implement the following script through your host microcontroller (pseudo-code example):

// Initialize DRV2605L (load settings from initial table)

I2C_Write(0x5A, 0x01, 0x04); // ATH mode by default

// When gaming event occurs (user presses button or game triggers event)

I2C_Write(0x5A, 0x01, 0x00); // Library mode

I2C_Write(0x5A, 0x0C, 0x01); // Trigger haptic event

Delay(20ms); // Allow the event vibration to complete

// If no further events, revert back to ATH

I2C_Write(0x5A, 0x01, 0x04); // Audio-to-Haptic mode

This script can be integrated into gaming handheld firmware for effective and seamless haptic experience control.